Variable condenser



Dec. 28 1926.

E. G. SHALKHAUSER VARIABLE CONDENSER 2 Sheets-Sheet 1 Filed August 27, 1926 \m\ V k g i lnxzzntrna. 57 fdalfiazmen Decu 28 1926.

E. G. SHALKHAUSER VARIABLE CONDENSER Filed August 27, 1926 2 Sheets-Sheet 2 l I l q I I l I I I I Patented Dec. 28, 1926.

UNITED STATES ERIC G. SHALKHAUSEB, F PEOBIA, ILLINOIS.

VARIABLE CONDENSER.

Application tiled August 27, 1926. Serial No. 131,907.

This invention relates to variable condensers, particularly such as are adapted to be used in radio frequency circuits of radio apparatus.

The invention is fully described in the following specification and shown in the accompanying drawings, in which:

' Figure 1 is a top plan View of a condenser embodying the invention; x In Fig. 2 is a vertical longitudinal section through the same on the line 22 of Fig. 3;

Fig. 3 is a front elevation of the device removed from a panel;

Fig. 4 is a front elevation of the dial 5 housing;

Fig. 5 is a sectional view through the dial housing on the line 55 of Fig. 4; and

Fig. 6 is a partial end elevation of the stator as viewed from the line 66 of Fig. 2.

The embodiment illustrated comprises a condenser frame made up of front and rear plates 10 and 11 having recesses 12 into which are fitted spacer bars 13 of a suitable non-conductor such as hard fiber, rubber or some of the phenolic condensation products which are now commonly used for such purposes. These are secured to the end plates 10 and 11 by means of screws 14 or the like.

A stator element A is secured between the spacer bars 13 by means of screws 15 and consists preferably of a casting having an internal screw thread which is adapted to receive the complementary screw threads of a rotor B which is mounted upon a shaft C 8 and which is fed into and out of the stator A by means of a screw D as the shaft C is turned and which is secured to the rear plate 11 by means of an extension 16 fastened through a hole 17 in the plate, and a nut 18 screwed upon the threaded outer end of said cxtension.

The screw D has a hollow center 19 in which is journalled the reduced end 20 of the shaft C. the other being also reduced at 21 and journalled in the front plate 10.

This shaft is turned by means of a knob E as shown in Fig. as will be later explained.

The rotor B is made conical in form as is shown in dotted lines in Fig. 2 in its outermost position and in full lines in its innermost" position. The screw threads of the rotor are thicker at the inside '22 than they are at the outside 23, while the internal threads of the stator are correspondingly shaped, being thicker at the outside 24 than they are at the inside 25 so that when the rotor B is turned to its full in position as shown in Fig. 2 in full lines, the rotor and stator are separated from each other by a small air gap which is preferably substantially uniform at all points throughout the screw threads.

The rotor is turned by means of a longitudinal keyway 26 in the enlarged portion 27 of the shaft C and is engaged by a key 28 extending inwardly from the hub 29 of the rotor B. This hub loosely surrounds the screw D but narrows at its inner end 30 and is provided with an internal thread 31 which engages the threaded member D. '70

It will be understood, of course, that the pitch of the threads D is the same as the pitch of the threads of the rotor B. As the shaft C is turned it will act through the keyway 2,6 of the key 28 to turn the rotor B and this will then be set in or out, depending upon which way the shaft C is turned, so as to move the rotor B into or out of the stator A.

The setting of the rotor 13 with respect to the stator A is accomplished by having; the nut 18 loosened and turning the screw D until the rotor B can readily be turned into the stator'A tov the full depth. The screw D is then turned so as to bring the threads of the rotor B midway between the internal threads of the stator A, the. outer edges 23 of the rotor threads being visible through the openings 32 in the shell or housing of the stator A. The nut 18 is then ad- .justed and the rotor can be fed into or of the stator by turning the shaft 21 since the pitch of the screw D is the same as the pitch of the screw threads of the rotor and the stator.

From the foregoing it will be apparent that due to the conical form of the stator and rotor the capacity of the condenser is, less as the thread of the rotor starts to enter the stator and builds up capacity more rapidly as the rotor nears its full-in position than would be the case were the threads of the stator and rotor of the same diameter throughout.

It will also be apparent that this effect is greatly increased by making the threads inclined so that they are thicker at their base and thinner at the edges. This tapering of the threads causes the surfaces of the threads to approach each other as the rotor is screwed in while the conical form of the internal and external screws provides a From the foregoing it will be clear that thecapacity is dependent upon three things;

namely, the length of the threads in overlapping position, the radio overlapping of these threads which varies due to the conlcal form and the distance betweenplates which varies due to the conical form and also tothe wedge-shaped screw threads.

This is of considerable advantage in a condenser for use in a radio frequency circuit for the reason that the rate of increase of capacity shall increase as the capacity itself increases.

Applicant preferably mounts his condenser upon a panel F by means of screws 33 as shown in Fig. 2. Figs. 4 and 5 show a preferred form of knob and dial which indicates the position of the rotor. The dial 34 hasa hub 35 which is secured to the extension 21 by means of a set-screw 36. The hub 35 is screw threaded to receive the knob E, the lower portion of the hub being turned and journalled in the dial housing 37 which is secured to the panel F by means of a screw 38. The-shaft C and the housing 37 are preferably tensioned by means of a flat spring 39 which is compressed by a nut 40 on the screw threaded hub 35.

The outer edge of the dial 34 is graduated as shown in Fig. 4, the graduation being readable through the window 41 in the housing 37. The dial 34 carries a pin 42 which operates the Geneva-gcar 43 which has a graduated dial 44 which has numbers indicating the number of threads of the screws which are in overlapping position. This dial is visible through the window 45 in the housing 37. Thus it will be seen that the lating said rotor and stator .from each other,

2. A variable condenser comprising a cone-shaped rotor rotatable about a central axis and having an exterior thread, a stator having a complementary hollow conical internally threaded space, and means for feed ing the rotor longitudinally of said axis whereby the threads are fed deeper radially into each other as the rotor is fed longitudinally into the stator, and means for insulating said rotor and stator from each other, said threads being thicker at the base than at the edge so as to cause the threaded surfaces of the rotor and stator to approach each other as the rotor is screwed into the stator and vice versa.

3. A variable condenser comprising a cone-shaped rotor rotatable about a central axis and having an exterior thread, a stator having a complementary hollow conical internally threaded space, means for feeding the rotor longitudinally of said axis whereby the threads are fed deeper radially into each other as the rotor is fed longitudinally into the stator, 'means for insulating said rotor and stator from each other, and means for indicating the number of turns the rotor is screwed into the stator.

4. A variable condenser comprising a cone-shaped rotor rotatable about a central axis and having an exterior thread, a stator having a complementary hollow conical internally threaded space, means for feeding the rotor longitudinally of said axis whereby the threads are fed deeper radially into each other as the rotor is fed longitudinally into the stator, means for insulating said rotor and stator from each other, and a Geneva-gear for indicating the number of turns the rotor is screwed into the stator.

In testimony whereof I hereunto set my hand this 17 day of August, 1926.

ERIC G. SHALKHAUSEI-I. 

